at the back of the cage. As the picture started, the figure was bent over an opened suitcase, stuffing into it bundles of bills. He straightened up and reached to the rack for more bills, and as he did so he faced the camera full for a moment. He picked up other bundles of bills, filled the suitcase, fastened it in a leisurely manner, opened the rear door of the cage and walked out.
"Again, please!" called Dr. Bird. "And stop when he faces us full."
The picture was repeated and stopped at the point indicated.
"Lights, please!" cried the doctor.
The lights flashed on and Dr. Bird rose to his feet, pulling up after him the wilted figure of a middle-aged man.
"Gentlemen," said the doctor in ringing tones, "allow me to present to you Professor James Kirkwood of the faculty of the Richton University, formerly known as James Collier of the Bureau of Standards, and robber of the First National Bank."
Detective-Captain Sturtevant jumped to his feet and cast a searching glance at the captive.
"He's the man all right," he cried. "Hang on to him until I get a wagon here!"
"Oh, shut up!" said Carnes. "He's under federal arrest just now, charged with the possession of narcotics. When we are through with him, you can have him if you want him."
"How did you get that picture, Doctor?" cried the cashier. "I watched that cage every minute during the morning and I'll swear that man never entered and stole that money as the picture shows, unless he managed to make himself invisible."
"YOU'RE closer to the truth than you suspect, Mr. Rogers," said Dr. Bird. "It is not quite a matter of invisibility, but something pretty close to it. It is a matter of catalysts."
"What kind of cats?" asked the cashier.
"Not cats, Mr. Rogers, catalysts. Catalysts is the name of a chemical reaction consisting essentially of a decomposition and a new combination effected by means of a catalyst which acts on the compound bodies in question, but which goes through the reaction itself unchanged. There are a great many of them which are used in the arts and in manufacturing, and while their action is not always clearly understood, the results are well known and can be banked on.
"One of the commonest instances of the use of a catalyst is the use of sponge platinum in the manufacture of sulphuric acid. I will not burden you with the details of the 'contact' process, as it is known, but the combination is effected by means of finely divided platinum which is neither changed, consumed or wasted during the process. While there are a number of other catalysts known, for instance iron in reactions in which metallic magnesium is concerned, the commonest are the metals of the platinum group.
"Less is known of the action of catalysts in the organic reactions, but it has been the subject of intensive study by Dr. Knolles of the Bureau of Standards for several years. His studies of the effects of different colored lights, that is, rays of different wave-lengths, on the reactions which constitute growth in plants have had a great effect on hothouse forcing of plants and promise to revolutionize the truck gardening industry. He has speeded up the rate of growth to as high as ten times the normal rate in some cases.
"A few years ago, he and his assistant, James Collier, turned their attention toward discovering a catalyst which would do for the metabolic reactions in animal life what his light rays did for plants. What his method was, I will not disclose for obvious reasons, but suffice it to say that he met with great success. He took a puppy and by treating it with his catalytic drugs, made it grow to maturity, pass through its entire normal life span, and die of old age in six months."
